Page 452 - Industrial Power Engineering and Applications Handbook

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Table 14.4 (Contd.)
(B) Control circuits
1
I Component 55 kW feeders 5.5 kW feeders
VAa Watt loss VA" Watt loss1 63/32A SFUfeeders
I QQ
Contactor coil 85 at 0.3 p.f. 25.5 15 at 0.35 p.f. 5.25
CT 7.Sb 7.5 5b 5
Ammeter 5b 5.0 5b 5 NIL
ON light 7b 7.0 7b 7
Auxiliary contactor 15 at 0.35 p.f. 5.25 -
Loss at 40°C Wd0 Total 50.25 Total 22.25

(I) loss at 90°C w,,, = w,,,[ 1 + wz0 (90 - 40)1 Vgo = 22.25[1+ 3.93 x 10-'(50)1
= 50.25 [I + 3.93 x IO-' (so)] = 26.62
= 60.12 for copper) or 2 feeders = 53.24
2 Control cables, 2.5 mm2 @ 10 dfeedel @ 5 m/ feeder
(copper flexible).
Cable resistance at 20°C NIL
(Table 13.15) Rkm 7.6 7.6
Control circuit current less than IA less than IA
x
x
7.6
:. Watt-loss at 20°C (For 1A) ~ 1 0.076 5 7.6 = 0.038 per feeder
=
1000 1000
(11) Watt loss at operating
temperature (90°C)
wgo = w20 [I 4- =20(90 - 20)] 1 x 0.076 [I + 3.93 x 10-'(70)] 2 x 0.038 [I + 3.93 x 10-3(70)]
= 0.097 = 2 x 0.048 = 0.096
Loss in control circuits (I + 11) I 60.22 53.34 I
Total loss in control circuits = 113.56 W (B)
If the loss in the control cables is small, this can be ignored for a quicker estimation of losses.
(C) Power cables (aluminium)
(mm2) 3 x 95 3x4 3'1, x 25
Average length from cable
gland to the power
terminals (m) 1 .5 2.0 2.5
Cable resistance at 20°C
(Table 13.15) Wkm 0.32 7.54 I .2
2
x
:.Watt loss at 20°C 1 x 3 x 110' x 1.5 0.32 2x3~12' x-x7.54 1 x 3 x 32' x 2.5 x 1.2
1000 1000 1000
= 17.42 = 13.03 = 9.22
Watt loss at, operating
temperature (90°C)
Wg" = W2" [ 1 + -20 (90 - 20) 17.42 (1 + 4.03 x IO-' x 70) 13.03(1 + 4.03 x IO-' x 70) 9.22(1 + 4.03 x x 70)
= 22.33 = 16.7 = 11.82
xz0 for aluminium from
Table 30.1
= 4.03 x lo-' per OC
Total loss in power cables = 50.85
Total watt losses A + B + C = 181.40 W
:.Heaters required for 180 W, which may be arranged in the sizes of 3 of SOW each and of 30 W (or as convenient) and located as shown
in Figure 14.2.
a From manufacturers' catalogues at 4OoC
We may consider these at unity p.f.